JPH0941225A - Production of silicon carbide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon carbide fiber having 1.00-1.10 atomic ratio of C/Si and a high strength and a high elasticity especially at a high temperature, and excellent in oxidation resistance and creep property at the high temperature. SOLUTION: This method for producing a silicon carbide fiber consists of the process of obtaining a primary burnt fiber with the primary burning of a fiber made as infusible by making the precursor fiber of an organic silicon- based polymer infusible, with a gradual temperature elevation, and the process of obtaining the silicon carbide fiber by the secondary burning of the primary burnt fiber. Although the primary burning is performed under at least one or more atmosphere selected from a hydrogen gas, a diluted hydrogen gas and an inert gas, it is preferably performed under the hydrogen gas or the diluted hydrogen gas atmosphere at least within a temperature range of 600-800 deg.C, and also the secondary burning is performed under a diluted hydrogen chloride gas or the diluted hydrogen gas atmosphere at 1500-2200 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION According to a conventional method for producing a SiC fiber, for example, the method disclosed in US Pat. No. 4,100,233, the C / Si atomic ratio is 1.31 or more and oxygen is O / Si. SiC fiber containing 0.35 or more in atomic ratio,
That is, only a SiC fiber containing a large amount of oxygen and excess carbon was obtained. Such SiC fiber has high temperature heat resistance,
There was a problem that the high temperature strength and the creep property at high temperature were deteriorated by oxygen and surplus carbon contained in the fiber.

The present invention relates to a method for producing silicon carbide fibers, and more specifically, it employs a hydrogen gas-containing atmosphere in the primary firing step and a hydrogen chloride gas or halogen gas-containing atmosphere at a certain high temperature in the secondary firing step. Accordingly, the present invention relates to a method for producing a silicon carbide fiber having a C / Si atomic ratio of 1.0 to 1.1 and being excellent in heat resistance, oxidation resistance and creep property particularly at high temperature.

[0003]

2. Description of the Related Art According to a conventional method for producing silicon carbide fiber (SiC fiber), for example, the method disclosed in US Pat. No. 4,100,233, the atomic ratio of carbon to silicon (C / S
Only SiC fibers having i) of 1.31 or more and oxygen containing 0.35 or more in oxygen / silicon atomic ratio (O / Si) were obtained.

When such a SiC fiber containing a large amount of oxygen and excess carbon is treated at a high temperature, silicon and carbon are oxidized by the oxygen contained in the fiber itself, even in an inert atmosphere. As a result, the fiber deteriorates, and there is a problem in that it is inferior in high temperature heat resistance, high temperature strength, and creep property at high temperature.

Conventionally, silicon carbide fibers are obtained by infusibilizing a precursor fiber obtained by spinning polycarbosilane or the like under certain conditions, and then firing by heating in an atmosphere of an inert gas such as nitrogen gas. Was manufactured. Also recently
The applicant has also proposed a firing method in an atmosphere containing hydrogen gas (for example, Japanese Patent Application No. 6-291956).
issue).

It is possible to control the C / Si atomic ratio to around 1 which is a stoichiometric composition and to reduce the oxygen content, by deoxidizing and decarbonizing by this firing in an atmosphere containing hydrogen gas. Became. However, since this calcination is performed at a high temperature, it is difficult to delicately control the reaction, and the decarbonization reaction often proceeds so much that the C / Si atomic ratio exceeds 1.

Since free silicon is present on the surface of the fibers having a C / Si atomic ratio of less than 1, when heat treatment is performed at a high temperature of 1500 ° C. or higher in air or an oxygen-containing atmosphere,
The free silicon reacted with oxygen to cause remarkable deterioration of the fiber, and the oxidation resistance was still insufficient. Further, even in a fiber having a C / Si atomic ratio of 1 or more, some free silicon exists on the surface thereof, and excess carbon exists inside,
Therefore, there is a problem that such conventional silicon carbide fibers are restricted in use at high temperatures.

In recent years, silicon carbide fibers have been expected as a constituent material for various members of high-temperature gas turbines, but conventional silicon carbide fibers have the above-mentioned problems, and also have high oxidation resistance and creep resistance at high temperatures. Since it is not enough, it cannot be put to practical use.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves these problems of the prior art, and the atomic ratio of carbon to silicon is 1.0 to.
It is 1.1, and an object thereof is to provide a method for producing a silicon carbide fiber which has a high strength and a high elastic modulus at a high temperature, as well as an excellent oxidation resistance and a creep property at a high temperature.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that, in addition to the conventional firing step, an atmosphere containing hydrogen chloride gas or halogen gas at a certain high temperature is used. The present invention has been accomplished by finding that the above object can be achieved by providing a secondary firing step used as a firing atmosphere.

That is, the method for producing a silicon carbide fiber according to the present invention comprises a step of primary firing of infusible fiber obtained by infusifying a precursor fiber of an organosilicon polymer at a temperature to obtain a primary fired fiber, A method comprising the step of secondarily firing a primary fired fiber to obtain a silicon carbide fiber, wherein the primary firing is performed in at least one atmosphere selected from hydrogen gas, diluted hydrogen gas and an inert gas, In a temperature range of at least 600 to 800 ° C., hydrogen gas or diluted hydrogen gas atmosphere is used, and the secondary firing is performed in a diluted hydrogen chloride gas or diluted halogen gas atmosphere.
It is a method for producing a silicon carbide fiber having an atomic ratio C / Si of carbon and silicon of 1.00 to 1.10.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The manufacturing method of the present invention will be described in more detail below.

In the present invention, a precursor fiber obtained by spinning an organosilicon polymer (polymer compound) is used. Examples of the organosilicon polymer used as a raw material include polycarbosilane, polysilazane, and polysiloxane. Further, as such an organic silicon-based polymer, in addition to carbon, silicon, oxygen and nitrogen,
A polymer containing a metal element such as boron, titanium, zirconium, or aluminum may be used. In addition, polycarbosilane fibers are generally used as the precursor fibers of the silicon carbide fibers.

The precursor fiber obtained by processing the above-mentioned organosilicon polymer into a fiber shape by a conventionally known spinning means such as melt spinning and dry spinning is then infusibilized. As the infusibilizing method, conventionally known methods such as a method utilizing a chemical reaction with oxygen, an oxide, an unsaturated hydrocarbon compound, and the like, and a method of causing a crosslinking reaction using various radiations such as an electron beam and ultraviolet rays. Is appropriately adopted. Further, various conditions at the time of infusibilization, for example, atmosphere, temperature, time, specific method and the like are appropriately selected according to the infusibilizing method to be adopted.

The infusibilized fiber is then subjected to a primary firing in a hydrogen gas or diluted hydrogen gas atmosphere at a temperature range of at least 600 to 800 ° C. while raising the temperature, whereby the C / Si atomic ratio is increased. Is 1.10 to 0.85
A primary fired fiber is obtained. That is, in the temperature range below 600 ° C. and above 800 ° C., primary firing may be performed in any atmosphere of hydrogen gas, diluted hydrogen gas, or inert gas. The primary firing start temperature is usually room temperature, and the end temperature is 1
200-1300 degreeC is preferable.

Examples of the inert gas include nitrogen gas, argon gas, helium gas and the like. The "diluted hydrogen gas atmosphere" referred to here is an atmosphere in which hydrogen gas and an inert gas are mixed, and examples of the inert gas include the above.

As an example of the above-mentioned primary calcination, first, there is a method in which all the primary calcination steps are performed in a diluted hydrogen gas atmosphere. The hydrogen gas content in this diluted hydrogen gas atmosphere is 10
vol. % Or more, preferably 50 to 70 vo
l. % Is optimal. The temperature rising rate is 10 to 1000 ° C.
/ Hr is preferred, room temperature to preferably maximum temperature 120
The temperature is raised to 0 to 1300 ° C., and if necessary, held for a certain period of time to complete the primary firing.

For example, if the hydrogen gas content in the atmosphere is 50
~ 70 vol. When set to%, room temperature is 1200 to
By firing up to 1300 ° C. at a heating rate of about 100 ° C./Hr, it is possible to obtain a primary fired fiber having a C / Si atomic ratio of 1.10 to 0.85. Needless to say, if the hydrogen gas content is lower than this, it is necessary to slow the temperature rising rate and perform the firing.

As another primary firing method, there is a method in which firing is started in a pure hydrogen gas atmosphere and the hydrogen gas atmosphere is switched to an inert gas atmosphere while the temperature is rising.
In order to set the C / Si atomic ratio to 1.10 to 0.85, this switching temperature needs to be 800 ° C. or higher, preferably 800 to 1200 ° C., and more preferably 800 to 9
50 ° C. Switching temperature to inert gas atmosphere is 8
This is because if the temperature is lower than 00 ° C., a slight decarbonization reaction occurs and a large amount of free carbon remains in the obtained silicon carbide fiber. Then, in the switched inert gas atmosphere, the maximum temperature is preferably raised to 1200 to 1300 ° C., and if necessary, held for a certain period of time to finish the primary firing. The rate of temperature increase is preferably 10 to 1000 ° C / Hr.

As an example, when the temperature for switching the hydrogen gas to the inert gas is set to 800 ° C., room temperature to 12
By firing at a temperature rising rate of about 100 ° C / Hr from 00 to 1300 ° C, the C / Si atomic ratio is 1.10 to 0.8.
5 primary calcined fibers are obtained. Needless to say, when the switching temperature is higher than this, the heating rate is increased to perform the firing.

As another primary firing method, 600 to 8
In the temperature range of 00 ° C., firing is performed in a hydrogen gas or diluted hydrogen gas atmosphere, and in the temperature range of room temperature to less than 600 ° C. and above 800 ° C. to completion of primary firing, an inert gas atmosphere is used. In this case, the temperature rising rate is 10 to 1000
℃ / Hr is preferred, room temperature to preferably maximum temperature 12
The temperature is raised to 00 to 1300 ° C., and if necessary, held for a certain period of time to finish the primary firing.

In the present invention, the desired primary fired fiber can be obtained by using any of the above methods. As another method, all primary firing may be performed only in a hydrogen gas atmosphere.

Thus, at least 6 of the primary firing step
By adopting a hydrogen gas or diluted hydrogen gas atmosphere having a reducing action in the temperature range of 00 to 800 ° C., the pyrolysis reaction and decarbonization reaction of the precursor fiber proceed. As a result, the chemical composition of the obtained primary fired fiber is controlled, that is, the excess carbon amount and oxygen amount are suppressed.

In this primary firing step, the time for holding the infusible fiber in a hydrogen gas or diluted hydrogen gas atmosphere,
Specific conditions such as temperature range, the amount of infusible fiber used,
According to various conditions such as hydrogen gas concentration, the C / Si atomic ratio of the obtained primary fired fiber is appropriately selected to be 1.10 to 0.85.

The fibers primarily fired as described above are
Finally, in a diluted hydrogen chloride gas atmosphere, secondary firing is performed at 1500 to 2200 ° C., which is a temperature near the melting point to the boiling point of silicon. As a result, free silicon on the surface of the primary fired fiber is removed, and a silicon carbide fiber having a C / Si atomic ratio of 1.00 to 1.10. Here, the “diluted hydrogen chloride gas atmosphere” means an atmosphere in which hydrogen chloride gas and an inert gas are mixed, and examples of the inert gas include nitrogen gas, argon gas, helium gas and the like.

The secondary firing in the present invention is performed by the following method.

First, one method is a so-called continuous method in which secondary firing is continuously performed in the furnace in which primary firing has been performed. The content of hydrogen chloride gas in the diluted hydrogen chloride gas atmosphere is 0.1 to 25 vol. %, That is, the mixing ratio of hydrogen chloride gas to inert gas is about 0.1 to 30 vo
l. % Is preferably set to 1500 to 2200 ° C.
Secondary firing is performed at any temperature between. The firing time is 1
0 second or more is preferable.

In addition to the above continuous method, the secondary baking may be performed in a furnace different from the primary baking, that is, a so-called batch method. In other words, in an inert gas atmosphere, the temperature is raised from room temperature to start secondary firing,
This is a method in which hydrogen chloride gas is caused to flow into the furnace at an arbitrary temperature between 2200 ° C. to form a diluted hydrogen chloride gas atmosphere, and secondary firing is performed for several hours. Then, after the secondary firing, the temperature is lowered to finish the production of the silicon carbide fiber. In this case, the hydrogen chloride gas content in the diluted hydrogen chloride gas atmosphere is 0.1 to 25 vol. %, Heating rate is 300 to 700
C / Hr is preferred.

As described above, first, the chemical composition of the fiber is adjusted by primary firing. Next, by secondary calcination at high temperature, the free silicon exuded on the fiber surface layer by primary calcination is melted or vaporized, and this reacts with hydrogen chloride contained in the secondary calcination atmosphere to be removed as silicon chloride. It is considered that finally, a silicon carbide fiber having a C / Si atomic ratio of 1.00 to 1.10 can be obtained. Due to this action, the obtained silicon carbide fiber is hardly deteriorated even when heat-treated at a high temperature. The above-mentioned secondary firing is
A halogen gas such as chlorine gas may be used instead of hydrogen chloride gas.

By introducing the step of performing the secondary calcination in the atmosphere containing hydrogen chloride or halogen gas as described above, excess silicon is removed, resulting in high elastic modulus, heat resistance, and acid resistance at high temperature. It is possible to obtain a silicon carbide fiber having excellent chemical conversion and creep properties.

[0031]

EXAMPLES The present invention will be described in more detail with reference to the following examples. C / Si in each table is atomic ratio, N ₂ /
HCl is by volume.

Example 1 and Comparative Examples 1 and 2 Polycarbosilane having the following basic skeleton and an average molecular weight of about 2000 was melt-spun to obtain a precursor fiber having a diameter of 12 to 14 μm.

[0033]

Embedded image Subsequently, the precursor fibers were infusibilized by the methods shown in Table 1 to obtain infusibilized fibers. The conditions for such infusibilizing treatment are as follows. (Electron beam infusibilization) Atmosphere: He, electron beam accelerating voltage: 2 MeV, electron beam current: 3 mA, irradiation time: 10 Hr (O ₂ infusibilization) Atmosphere: Air, heating rate: 10 ° C./Hr, maximum temperature:
200 ° C. Next, each of the infusible fibers was subjected to 1 under the conditions shown in Table 1.
The temperature was raised to 300 ° C and primary firing was performed to obtain a primary fired fiber.
The rate of temperature rise in such a firing treatment is 100 ° C./Hr.

Finally, each of the above primary fired fibers is shown in Table 1.
Secondary firing was performed under the conditions shown in to obtain silicon carbide fibers. Table 1 shows the C / Si atomic ratio, tensile strength and tensile elastic modulus of the obtained silicon carbide fiber.

[0035]

[Table 1] From this table 1, the secondary firing was performed in an atmosphere containing hydrogen chloride gas 1
It was found that the silicon carbide fiber of Example 1 made at 800 ° C. had a higher tensile elastic modulus than those of Comparative Examples 1-2.

Next, the silicon carbide fiber thus obtained was subjected to a heat resistance test, an oxidation resistance test and a high temperature creep test by the following methods. Table 2 shows the results. [Heat Resistance Test] Each of the silicon carbide fibers was exposed to argon gas atmosphere at 1800 ° C. for 1 hour, and the tensile strength was measured. [Oxidation resistance test] Silicon carbide fibers in air 1
The tensile strength after exposure to a temperature of 400 ° C. for 10 hours was measured, and the oxidation resistance was evaluated by obtaining the ratio of this tensile strength and the tensile strength before the test. [High temperature resistance creep test] 12 silicon carbide fibers each
The sample was exposed to a temperature of 00 ° C. for 1 hour, a high temperature creep resistance test was performed, and the stress relaxation ratio was measured.

[0037]

[Table 2] From this Table 2, the silicon carbide fiber of Example 1 using the hydrogen chloride gas-containing atmosphere in the secondary firing has higher heat resistance and oxidation resistance than Comparative Examples 1 and 2 using the hydrogen chloride gas-free atmosphere. It was found that both the heat resistance and the high temperature creep resistance were excellent. In Table 1, also in Example 1 in which the tensile strength is slightly inferior to that of Comparative Examples 1 and 2, the tensile strength after the oxidation resistance test also shows a high value, and thus the strength ratio before and after the test also retains a high value. Was.

Therefore, the silicon carbide fiber obtained by the present invention can be sufficiently used in the air at about 1400 ° C., and can withstand use in an inert atmosphere at a high temperature of about 1800 ° C. It has been found.

Examples 2 to 4 and Comparative Example 3 Using the same polycarbosilane as that used in Example 1 as a raw material, the steps up to the primary firing were carried out by the following common methods. Next, as shown in Table 3, secondary firing was performed at 1800 ° C. for 10 seconds while changing only the mixing ratio of hydrogen chloride gas in the atmosphere, and Table 3 shows the characteristics of the resulting silicon carbide fibers. Indicated. Infusibilization; electron beam infusibilization primary firing; hydrogen gas atmosphere from room temperature to 800 ° C,
Argon gas atmosphere from 800 ° C. to 1300 ° C. (C / Si = 1.04 after primary firing) Note that other detailed conditions were in accordance with Example 1.

[0040]

[Table 3] From Table 3, first, the silicon carbide fiber of Comparative Example 3 obtained by secondary firing in an atmosphere not containing hydrogen chloride was
It was found that the strength was significantly deteriorated. In addition, Examples 2 to 4
The secondary firing was performed at 1800 ° C. in an atmosphere containing hydrogen chloride gas.
-10 vol. In the concentration range of%, the higher the concentration, the higher the tensile strength and tensile modulus. Further, the hydrogen chloride gas concentration is 10 vol. %, It was found that the heat resistance at 1800 ° C. or higher was also excellent.

Examples 5 to 7 and Comparative Examples 4 to 6 The same polycarbosilane as that used in Example 1 was used as a raw material and melt-spun. Then, the precursor fibers obtained respectively were subjected to the conditions shown in Table 4. Infusibilization and primary firing were performed. The other conditions were in accordance with Example 1. Then, the obtained primary fired fiber was subjected to secondary firing for 10 seconds in the atmosphere and temperature shown in Table 4.

Table 4 shows the results of comparing the appearances of the silicon carbide fibers due to the difference in the temperature and the atmosphere of the secondary firing. In the table, an atmosphere of only nitrogen gas was used as a comparative example, and hydrogen chloride gas was added at 10 vol. % Atmosphere is shown as an example. Further, the results are shown as Comparative Examples 4 to 6 and Examples 5 to 7 depending on the difference in the temperature of the secondary firing. The symbols in the table qualitatively represent the strength of the fiber, and ○ means good, Δ means weak, and x means brittle and weak.

[0043]

[Table 4] From Table 4, the mixing effect of hydrogen chloride gas in the secondary firing is clear. In each of the comparative examples that were subjected to the secondary firing under a nitrogen atmosphere, only significantly deteriorated silicon carbide fibers were obtained, while in the case of each of the examples in which hydrogen chloride was mixed and the secondary firing was performed, black- A good brown fiber was obtained. It is considered that this is because the free silicon existing in the surface layer of the fiber reacted with hydrogen chloride to form silicon chloride and was removed. However, at 2000 ° C or higher, the strength is slightly lowered.

[0044]

As described above, according to the production method of the present invention, the atomic ratio of carbon to silicon is 1.0 to 1.1, and the high strength and high elastic modulus are obtained even at high temperature. Further, it becomes possible to obtain a silicon carbide fiber having excellent oxidation resistance and creep resistance at high temperatures.

Claims (4)

[Claims] 1. A step of primary-firing the infusible fiber obtained by infusibilizing the precursor fiber of the organosilicon-based polymer while raising the temperature to obtain a primary-firing fiber, and further secondary-firing the primary-firing fiber to carbonize it. A method for producing silicon carbide fibers, comprising the step of obtaining silicon fibers, wherein the primary firing is performed in at least one atmosphere selected from hydrogen gas, diluted hydrogen gas and inert gas,
Carbon and silicon are obtained by performing the secondary calcination in a hydrogen gas or diluted hydrogen gas atmosphere at least in the temperature range of 600 to 800 ° C., and by performing the secondary firing at 1500 to 2200 ° C. in a diluted hydrogen chloride gas or diluted halogen gas atmosphere. Atomic ratio C / Si of 1.00 to 1.1
A method for producing 0 silicon carbide fibers. 2. The content of hydrogen chloride gas or halogen gas in the atmosphere of the secondary firing is 0.1 to 25 vol.
%. The method of claim 1 which is%. 3. The temperature rising rate of the primary firing is 10 to 100.
The method according to claim 1 or 2, wherein the temperature is 0 ° C / Hr. 4. The method according to claim 1, wherein the primary firing is completed at 1200 to 1300 ° C.